An oil windfall offers Gulf states one last chance to splurge

In the north-western corner of Saudi Arabia, not far from the mouth of the Gulf of Aqaba, sits a patch of mostly bare desert—the ostensible location of Neom. This would-be city is intended to be a bold step into the future, and the showpiece of the kingdom’s attempt to diversify its economy away from oil. There has been talk of robots doing menial work, beaches lined with crushed marble and fleets of drones forming an artificial moon. One recent whim is to create the world’s longest buildings; like skyscrapers laid flat, these self-contained ecosystems would stretch for more than 100 miles. Estimates suggest the city could cost as much as $500bn.